The purpose of this proposal is to study the ionic currents in the Ascidian oocyte membrane that are activated by the fertilizing spermatozoon. The research shall correlate the apearance of sperm-activated channels with the fertilization potential, characterize the channels with regard to ion specificity and kinetics, and test the hypothesis that the channels are activated from the cytoplasmic side of the oocyte membrane by Ca. The experiments make use of Ascidians because the dechorinated oocytes are easily patch-clamped and because Ascidian oocytes lack cortical granules: Single-channel recording provides a molecular description of the sperm-activated currents, and the absence of cortical granules elininates a potential mechanism for the introduction of channels into the oocyte membrane. In addition, the patch-clamp technique isolates a defined area of oocyte membrane, and we shall use this feature to restrict the site of gamete interaction by putting sperm in the recording pipette. This experiment, in combination with patch experiments in which sperm are added to the bath, and in combination with the whole-cell recording of fertilization currents, will help to determine where the channels are located, how many channels are activated by the fertilizing spermatozoon, and from which side of the oocyte membrane the channels are opened. The overall aim is to learn how sperm-activated channels interrelate with other events that occur during fertilization, and to determine the primary trigger of oocyte activation. These experiments will aid in the overall understanding of how sperm activate oocytes, and they will further the science and the experimental control of in vitro fertilization.